Alpha hydroxy acids (AHAs) have been proven to deliver cosmetic benefits, such as improvement in the appearance of photodamaged or naturally aged skin, skin lightening, treatment of age spots, etc. Unfortunately, their use at high concentrations may occasionally be associated with skin irritation, e.g. skin redness and stinging sensation upon application. See e.g. Kligman A. M., J. Geriatr. Dermatol. 1997; 5(3): 128-131). The irritation can be ameliorated by lowering the amount of an active ingredient in the composition or by reducing the active's penetration through the skin. A serious drawback of both approaches is that the efficacy is impaired. The AHA irritation can be reduced by raising the composition's pH but this method yields reduced efficacy due to a decreased AHA penetration through the skin. It is desirable to reduce or eliminate the irritation potential of AHAs while maintaining their efficacy.
European Patent Application 0631722 (Johnson & Johnson) discloses the use of glycolic acid to reduce irritation of the skin by retinol. U.S. Pat. No. 5,516,793 (Duffy) discloses the use of ascorbic acid to ameliorate the irritation caused by various topical ingredients, including AHAs.
Use of oils rich in petroselinic acid e.g coriander seed oil in cosmetic compositions for skin has been disclosed (EP 0709084 A2). EP 0709084 teaches the use of coriander seed oil as a moisturizing agent but does not disclose the property of petroselinic acid to reduce irritation. In addition, the optional presence of various additives is mentioned, e.g. keratolytic agents such as hydroxyacids (n-octanoyl 5-salicylic acid). Salicylic acid is a beta-hydroxy acid, which is known to act in a manner different from alpha hydroxy acids and is believed to be less irritating.
The art discussed above does not disclose combinations of AHAs and coriander seed oil or petroselinic acid in cosmetic compositions and does not appear to teach the use of petroselinic acid to reduce irritation or sting associated with the use of AHAs.